The present invention relates generally to the field of electromagnetic nerve stimulation. More specifically the present invention relates to a method and apparatus for nerve stimulation using optimal efficient parameters for the electrical charging circuit.
Electrical stimulation has been successfully tested clinically for multiple applications tracing its roots back to the late 1800""s where it was applied in the stimulation of the peripheral facial muscles by George Duchenne de Boulogne, see M. S. George, xe2x80x9cRe-animating the face: early writings by Duchenne and Darwin on the neurology of facial emotion expressionxe2x80x9d, J. Hist. Neurology, vol.2, 1994, pp. 1-13. Since then it has been used for muscle rehabilitation (see e.g., G. A. Dudley, xe2x80x9cIs electrical stimulation applicable to increase strength and power in normal humans?xe2x80x9d, in Human Muscular Function During Dynamic Exercise, ed. by P. Marconnet, B. Saltin, P. Komi, and J. Pootmans, Karger Book Series: Medicine and Sport Science, Karger Publications, Basel, 1996, pp. 71-81), bed sore treatment, incontinence, and general diagnostics to mention only a few of its applications. Excitations that are repeated demand higher efficiency. Greater efficiency translates into lighter and smaller power supplies, and longer life for implantable devices.
Magnetic stimulation is only now catching up to electrical stimulation in terms of clinical uses. Early uses of MS were principally devoted to diagnostics, a good review of which is found in E. M. Wasserman, L. M. McShane, M. Hallett, and L. G. Cohen, xe2x80x9cNoninvasive mapping of muscle representations in human cortexxe2x80x9d, Electroencephalography and Clinical Neurophysiology, vol. 85, 1992, pp. 1-8. More recently rapid transcranial magnetic stimulation (rTMS) is being used in speech diagnosis, see e.g., C. M. Epstein, J. K. Lah, K. Meador, J. D. Weissman, L. E. Gaitan, B. Dihenia, xe2x80x9cOptimum stimulus parameters for lateralized suppression of speech with magnetic brain stimulationxe2x80x9d, Neurology, vol. 44, 1994, pp. 269-273. It is also being successful employed in the treatment of severe clinical depression, see e.g., A. Fleischman, K. Prolov, J. Abarbanel, R. H. Belmaker, xe2x80x9cEffect of Transcranial magnetic stimulation on behavioral models of depressionxe2x80x9d, Brain Research, vol. 699, 1995, pp. 130-132 and B. Greenberg, U. McCann, J. Benjamin, D. Murphy, xe2x80x9cRepetitive TMS as a probe in Anxiety Disorders: Theoretical Considerations and Case Reportsxe2x80x9d, CNS Spectrums, vol.2, no. 1, 1997, pp. 47-52. As more applications of the rapid magnetic stimulation surface, the issues of efficiency both within the body and the stimulation circuit arise.
In 1991 Barker, et. al., wrote a study on the effect of waveform efficiency in determining neural membrane efficiency. See A. Barker, C. Graham, and I. Freeston, xe2x80x9cMagnetic nerve stimulation: the effect of waveform on efficiency, determination of neural time constants, and the measurement of stimulator outputxe2x80x9d, Magnetic Motor Stimulation: Basic Principles and Clinical Experience, EEG Supplemental 43, 1991, pp. 221-237. Following the suggestion of Plonsey, R. Plonsey, Bioelectrical Phenomena, McGraw Hill, New. York, 1969, Barker et. al. modeled the nerve membrane as a parallel capacitance and resistance, with an intracellular and extracellular resistance providing the closure path for any induced or injected currents. The energy necessary to achieve threshold stimulation was measured as a function of B field rise time. Threshold stimulation energy continued to drop with reduced rise time of the resonance frequency of the magnetic stimulator. Their methods were useful in predicting nerve membrane time constants.
Magnetic stimulation requires moving enough charge through an electrically sensitive nerve membrane to depolarize it, see, e.g. John Cadwell, xe2x80x9cOptimizing Magnetic Stimulator Designxe2x80x9d, Magnetic Motor Stimulation: Basic Principles and Clinical Experience, EEG Supplement 43, 1991, pp. 238-248; this means that the membrane voltage must be increased from its normal resting negative potential. Many authors have attempted to offer guidelines for producing energy efficient stimulation coils, as well in the modeling of these coils. See e.g., G. A. Mouchawar, J. A. Nyenhuis, J. D. Bourland, and L. A. Geddes, xe2x80x9cGuidelines for energy efficient coils: coils designed for magnetic stimulation of the heartxe2x80x9d, Magnetic Motor Stimulation: Basic Principles and Clinical Experience, EEG Supplement 43, 1991, pp. 255-267; C. W. Hess, K. M. Rosler, R. O. Heckmann, H. P. Ludin, xe2x80x9cMagnetic Stimulation of the Human Brain: Influence of size and shape of the stimulating coilxe2x80x9d, Motor Disturbances II, Academic Press Limited, London, U.K. 1990, pp. 31-42; A. Cantano, P. Noel, xe2x80x9cTranscranial Magnetic Stimulation: Interest in the excitation thresholdxe2x80x9d, Acta Neurologica Belgica, vol. 97, 1997, p. 61; G. Cerri, R. Deleo, F. Moglie, A. Schiavoni, xe2x80x9cAn accurate 3-D model for magnetic stimulation of the brain cortexxe2x80x9d, Journal of Medical Engineering and Technology, Vol. 1, 1995, pp. 7-16. Roth and Basser, B. J. Roth and P. J. Basser, xe2x80x9cA model of the stimulation of a nerve fiber by electromagnetic inductionxe2x80x9d, IEEE Transactions on Biomedical Engineering, vol. 37, 1990, pp. 588-596, were among the first to actually model the stimulation of a single fiber by electromagnetic induction. However, there is still a substantial interest in the art for a method of nerve stimulation using optimal efficient parameters of the electrical charging circuit.
It is an object of the present invention to provide a method for nerve stimulation wherein a coil design and its parameters are chosen from coupling analytically the electromagnetic circuit to that within the nerve.
Other objects, advantages and features of this invention will be more apparent hereinafter.
The present invention provides a method for nerve cell stimulation, comprising selecting an optimal frequency of a coupled magnetic circuit for construction of a magnetic nerve stimulator, selecting an optimal reluctance of a coupled magnetic circuit for construction of a magnetic nerve stimulator, selecting an optimal capacitance of a coupled magnetic circuit for construction of a magnetic nerve stimulator, and selecting an optimal winding resistance of a coupled magnetic circuit for construction of a magnetic nerve stimulator. In the preferred embodiment, the optimal frequency, optimal reluctance, optimal capacitance and/or the optimal winding resistance are selected to maximize stimulation of a peripheral nerve cell, or any other type of nerve cell, using the methods provided herein.